Multi-user MIMO (multi-user multi-input multi-output, hereinafter referred to as “MU-MIMO”) refers to a technology in which a transmitter simultaneously transmits different data to a plurality of terminals using the same spectrum in an environment where the transmitter having multiple antennas communicates with a plurality of receivers each having at least one antenna.
In order to materialize the MU-MIMO technology, the transmitter must include multiple transmitting antennas. The transmitter including multiple antennas needs to recognize a channel status information transmitter (CSIT) between an individual transmitting antenna and an individual receiving antenna to transmit different data to a plurality of receivers by using the same spectrum.
The transmitter recognizes the CSIT through CSIT feedback of the receiver, or acquires the CSIT by using a sounding channel transmitted from the receiver.
The MU-MIMO technology is classified into open loop MU-MIMO (OL MU-MIMO) that does not need the CSIT and closed loop MU-MIMO (CL MU-MIMO) that needs the CSIT. Further, the CL MU-MIMO is classified into partial CSIT MU-MIMO and full CSIT MU-MIMO according to the degree of CSIT. The full CSIT MU-MIMO is classified into a linear type and a non-linear type.
The performance of the CL MU-MIMO is better than that of the OL MU-MIMO. Further, as for the CL MU-MIMO, the performance of the full CSIT MU-MIMO is better than that of the partial CSIT MU-MIMO. However, the full CSIT MU-MIMO requires much more feedback than the partial CSIT MU-MIMO for the receiver to transmit the CSIT to the transmitter.
The full CSIT MU-MIMO is classified into the linear type and the non-linear type. In this case, the non-linear type provides much better performance than the linear type, but requires significant complexity for materialization.
An exemplary algorithm of the linear MU-MIMO includes channel inversion (hereinafter referred to as CI) and regularized channel inversion (hereinafter referred to as RI), and an exemplary algorithm of the non-linear MU-MIMO includes dirty paper coding (DPC), sphere encoding, and transmission vertical Bell Lab layered space time (VBLAST). The transmission VBLAST includes a transmitter to which the VBLAST is applied. Therefore, since interference cancellation is applied to the transmitter, the transmission VBLAST is considered to be an actually applied type of DPC.
FIG. 1 is a diagram showing SER performances of CI, RI, sphere encoding, and transmission VBLAST MU-MIMO algorithms. FIG. 1 shows a case in which different data is transmitted using the same spectrum by applying CI, RI, sphere encoding, and transmission VBLAST MU-MIMO algorithms, and 16QAM is used as the modulation method. Referring to FIG. 1, it is understood that the performance of the non-linear MU-MIMO is better than that of the linear MU-MIMO, and the sphere encoder has much better performance than the transmission VBLAST. However, the complexity of the sphere encoder is too high to be materialized.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.